On the Adaptive Tracking Control of 3-D Overhead Crane Systems

For low cost, easy assembly and less maintenance, overhead crane systems have been widely used for material transportation in many industrial applications. Due to the requirements of high positioning accuracy, small swing angle, short transportation time, and high safety, both motion and stabilization control for an overhead crane system becomes an interesting issue in the field of control technology development. Since the overhead crane system is underactuated with respect to the sway motion, it is very difficult to operate an overhead traveling crane automatically in a desired manner. In general, human drivers, often assisted by automatic anti-sway system, are always involved in the operation of overhead crane systems, and the resulting performance, in terms of swiftness and safety, heavily depends on their experience and capability. For this reason, a growing interest is arising about the design of automatic control systems for overhead cranes. However, severely nonlinear dynamic properties as well as lack of actual control input for the sway motion might bring about undesired significant sway oscillations, especially at take-off and arrival phases. In addition, these undesirable phenomena would also make the conventional control strategies fail to achieve the goal. Hence, the overhead crane systems belong to the category of incomplete control system, which only allow a limited number of inputs to control more outputs. In such a case, the uncontrollable oscillations might cause severe stability and safety problems, and would strongly constrain the operation efficiency as well as the application domain. Furthermore, an overhead crane system may experience a range of parameter variations under different loading condition. Therefore, a robust and delicate controller, which is able to diminish these unfavorable sway and uncertainties, needs to be developed not only to enhance both efficiency and safety, but to make the system more applicable to other engineering scopes. The overhead crane system is non-minimum phase (or has unstable zeros in linear case) if a nonlinear state feedback can hold the system output identically zero while the internal dynamics become unstable. Output tracking control of non-minimum phase systems is a highly challenging problem encountered in many practical engineering applications such as aircraft control [1], marine vehicle control [2], flexible link manipulator control [3], inverted pendulum system control [4]. The non-minimum phase property has long been recognized to be a major obstacle in many control problems. It is well known that unstable zeros cannot